Laminates having polyethylene coated on a paper substrate are used, for example, as containers for packaging in various fields such as foods.
However, polyethylene is excellent in water vapor barrier properties, but poor in gas barrier properties. To compensate for this nature, further lamination of polyethylene terephthalate having excellent gas barrier properties can be conceived as an excellent means of ensuring storage characteristics and aroma retaining properties for use in food packaging.
When the laminate is to be used as a base material for a packaging container, the outer layer of the laminate needs to have heat sealability. Conventional working methods, however, have used a stretched polyethylene terephthalate film, which is not heat sealable. For use as a base material for a packaging container, therefore, the laminate has required that a polyethylene layer be further coated on the polyethylene terephthalate layer by lamination or the like.
To laminate the stretched polyethylene terephthalate film, moreover, it is necessary to add an adhesive layer. Since the adhesive is used, however, this lamination method has involved the drawback of increasing the cost. Furthermore, the problem has been posed that an organic solvent or the like used in the adhesive remains.
Patent Document 1 discloses a working method which comprises adhering a polyethylene terephthalate layer and a polyethylene layer to a paper substrate without using the adhesive.